The invention generally relates to a method an apparatus for attaching the lid portion to the body portion of a metallic container, particularly a metallic food container such as an aluminum beverage can.
Metallic containers, particularly those intended for food products, must be structurally robust, be made from materials compatible with food products, and generally incorporate internal coatings to make them suitable for food contents. Generally, metallic food containers, such as carbonated beverage cans, have a pre-formed body portion and a pre-formed lid portion that is attached to the body portion after the beverage is placed therein. The body portion is usually formed from a single piece of suitable metallic material, such as aluminum, and is shaped by stamping, drawing, ironing, and/or other suitable metal forming process. The lid portion is formed in much the same manner. The body portion can be very thin after forming, and therefore, the lid portion desirably contributes to the structural rigidity for the finished container. The lid portion can be made from a material that is relatively harder than the body portion.
One known method of attaching the lid portion onto the body portion of the metallic container involves rolling or curling parallel flange portions of the lid and the body portion onto each other to form a lip seam. This process generally provides a good seal, and does not compromise the integrity of any coatings that may be placed on the interior of the metallic container. A variety of coatings can be used on the interior surfaces of the lid portion and the body portion of the container, which are preferably satisfactory for food contact, to prevent corrosion of the inner surface of the metallic food container and to prevent the metal from contaminating the taste of the food placed therein. The coating can be any of the materials identified, for example, in U.S. Pat. No. 5,739,215, which are hereby incorporated by reference. Typically, the body portion and the lid portion have the inner surfaces coated prior to the lid portion being attached to the body portion. Therefore, any attachment technique must account for and accommodate the coating.
By rolling the edges of the lid portion and the body portion onto one another, a tight seal is formed, and the coating is not compromised. However, this method of attachment requires extra metallic material to allow for portions to be rolled over onto one another in this manner. Additionally, typically in this process a vinyl seal or gasket can be placed between the edges of the lid portion and the body portion before they are rolled onto one another. This gasket material helps insure an adequate seal.
Other techniques can be used to reduce the amount of metallic material by directly connecting the edges by welding or soldering the edges together, by a process such as laser welding. This process will also provide a sealed attachment, however the temperatures necessary for this type of welding are high enough to compromise or destroy any coating placed on the inner surface of the body portion and the lid portion. This leaves an uncoated region immediately adjacent the area of the weld. Still other methods may use an intermediate material, with a lower melting point, between the lid portion and the body portion, to allow the lid portion and the body portion to be welded together, via the intermediate material, at a lower temperature.
Further, the processes discussed above, either rolling the edges of the lid portion and the body portion over onto one another, or welding the edges together require significant time to complete, thereby making the manufacture of these metallic containers more costly. The lid is generally attached to the body of the metallic container after the contents of the container have been placed therein. In the case of a carbonated beverage, as soon as a seal forms between the lid and the body of the metallic container, pressure will start to build within the container. This can cause carbonated beverage to be pushed between the lid and the body as the seal is being formed, thereby compromising the quality of the seal. Also, specifically with carbonated beverages, the portion of the beverage that leaks from within the container during the process of attachment makes a mess within the manufacturing facility.
Therefore, there is a need for an apparatus and method of forming a metallic container that will allow for a reduction in the amount of material used while providing a sealed attachment between the lid portion and the body portion without compromising any food compatible coatings placed on the inner surfaces of the lid portion and the body portion. Furthermore, there is a need for an apparatus and method of forming a metallic container that will reduce the cycle time of prior methods used to attach the lid to the body of a metallic container.